Challenging Popular Assumptions About Influenza

Hope-Simpson questioned other beliefs about the nature of influenza. “Epidemics of influenza often occur contemporaneously at the same latitude, even in localities widely separated by longitude,” he noted.8 But if outbreaks occur simultaneously in widely separated areas, how can person-to-person transmission be responsible?

Much has been made of the potential dangers of quickly transmitted infection, due to modern modes of transportation. However, through careful examination of ancient records, Hope-Simpson showed that virtually simultaneous outbreaks occurred in England long before the advent of modern roads, let alone continent-spanning jet-liners. This challenged the fundamental assumption that influenza is transmitted in a chain from one patient to another. Could it be that the flu virus lies dormant in a range of potential hosts, until some “seasonal stimulus” promotes its infectivity among these unwitting carriers?

Back in California, Dr. Cannell could not help but wonder whether vitamin D played a role in his patients’ evident immunity to the flu. He knew several things that Hope-Simpson did not. For one, scientists now know that influenza infection prompts white blood cells known as macrophages to release immune system chemicals called cytokines and chemokines, which promote inflammation. Furthermore, scientists now know that the virus responsible for 1918’s devastating global influenza pandemic was especially effective in stimulating the release of cytokines by macrophages.10 In fact, the severity of the resulting illness is believed to be proportional to a flu virus’s ability to evoke cytokine production. In bird flu, for instance, this response can be overwhelming, resulting in death.11,12 Dr. Cannell also knew that research has recently shown that vitamin D modulates macrophages’ production of chemokines and cytokines, in effect preventing them from overreacting to infectious stimuli and causing serious manifestations of viral infection.13,14

Vitamin D’s Role in Bolstering Immunity

Nor did Hope-Simpson have knowledge of another recently reported phenomenon. In the past few years, several independent researchers have shown that vitamin D significantly enhances the genetic expression of antimicrobial peptides in human monocytes (precursors to macrophages), neutrophils, and other immune system cells.15,16 These antimicrobial proteins help to destroy invading infectious microbes. With their broad-spectrum activity, they are capable of killing everything from bacteria to viruses. They have been shown to be an important part of the respiratory tract’s defense against invaders, and likewise show promise in fighting the influenza virus.17-19

For Dr. Cannell, these various clues led to one inescapable conclusion: vitamin D—which is produced when the skin is exposed to summer sunlight, and which, conversely, declines in winter—plays a critical role in our vulnerability to influenza infection. In fact, vitamin D must surely be Hope-Simpson’s mysterious “seasonal stimulus.” Dr. Cannell consulted a number of leading vitamin D researchers, all of whom agreed with his conclusions. They include researchers from such venerable institutions as the National Institutes of Health and the Harvard School of Public Health. One of these scientists, Dr. Michael F. Holick, has been studying vitamin D for three decades.1,7,20

In an interview with Life Extension, Dr. Holick alluded to the special relationship between vitamin D and the body’s primary immune system defenders, the macrophages. “What intrigues me the most,” Dr. Holick noted, “is that we’ve always known that macrophages activate vitamin D.” The form of vitamin D generated through the skin’s interaction with ultraviolet B radiation (from sunshine or artificial sources) is a pre-hormone. It must be converted in the body to its active hormone form, called 1,25-dihydroxyvitamin D3. An intermediary form, known as 25-hydroxyvitamin D, is the major circulating form of vitamin D, and is measured to determine vitamin D status.20

Vitamin D’s Far-Ranging Effects on Disease Prevention

Most of this activation of vitamin D occurs in the liver and kidneys. However, the fact that macrophages facilitate the conversion of circulating vitamin D to its active form,20 and that activated vitamin D in turn regulates the activity of macrophages, suggests an important relationship between the two.

Dr. Holick notes that vitamin D receptors have been identified in virtually every cell in the body. “It’s one of the earliest vitamins,” he says. “It was made by phytoplankton (microscopic aquatic plants such as algae) 750 million years ago.” He believes that vitamin D plays an important role in many aspects of health. “If you live at higher latitudes where less vitamin D is available from sunshine, you’re more likely to suffer from diabetes, multiple sclerosis, and colon, breast, prostate, and pancreatic cancers,” he says. “Even hypertension is associated with latitude. Patients exposed to sunlight increase their vitamin D levels, and their blood pressure comes down.”

Dr. Holick has published numerous papers detailing the relationship between inadequate vitamin D levels and increased risk of diseases ranging from osteoporosis and arthritis to cardiovascular disease and cancers.21,22 “Activated vitamin D is one of the most potent inhibitors of cell growth,” he notes, a fact that may explain its importance in cancer prevention. “I don’t see any downside to taking pharmaceutical levels of vitamin D to fight prostate cancer,” he adds.

The Importance of Vitamin D Supplements

The bottom line is that far too many people are deficient in vitamin D,22,23 especially the elderly.24 Unfortunately, by following well-intentioned advice to minimize their exposure to the sun, aging adults may greatly diminish their ability to manufacture optimal levels of vitamin D, particularly compared to young people. This could put them at increased risk of contracting the flu.

Although Dr. Holick serves on the board responsible for amending existing government recommendations for vitamin D intake, he thinks it will be at least another four years before the government publishes new recommendations aimed at increasing vitamin D intake to adequate levels. According to Dr. Holick, there is simply too much data being generated too quickly, by researchers around the world, for committee members to evaluate it any faster.

Nevertheless, he strongly advises aging adults to begin increasing their supplemental intake of vitamin D now, especially in winter, when sunlight exposure at higher latitudes is insufficient to produce adequate vitamin D levels naturally. “Most people should supplement with vitamin D,” says Dr. Holick. “It’s perfectly safe to take, and is likely to have a benefit for all aspects of health.”

Dr. Holick anticipates that if enough people get the message, we are likely to see a noticeable drop in everything from cancer cases to flu outbreaks. “It would be quite amazing,” he says. “It might very well markedly decrease a person’s risk.” Dr. Holick himself takes 1000 IU of vitamin D every day.

Dr. Cannell’s approach to vitamin D for disease prevention is even more aggressive. He and his family members take 5000 IU of supplemental vitamin D daily during the winter months. “The implications are breathtaking,” says Dr. Cannell. “The best thing may be not to stock up on antiviral drugs, but to get some sunshine. Should you go into the flu season vitamin D deficient? No. It’s a widespread problem, and it should be addressed.”

The intriguing theory that vitamin D may help prevent or arrest viral respiratory infections has tremendous potential in helping million of people avert these potentially deadly outbreaks. To date, however, no interventional studies in humans have been conducted. Such trials are sorely needed to assess vitamin D’s efficacy in preventing or treating influenza.

In the meantime, however, all health-conscious people would be well advised to optimize their daily intake of vitamin D, particularly during the winter months. This low-cost dietary supplement may just be the best possible medicine for guarding against the flu virus and bolstering your protection against a host of age-related afflictions.